The invention relates to a headbox of a paper and board making machine and, in particular, a hydraulic headbox comprising an inlet header section with a manifold tube section and an equalizing chamber in the stock suspension flow route, a turbulence generator section following the equalizing chamber, after which a tapered slice section is located, through which the stock suspension is discharged onto the wire.
It is known in paper and board making that the instantaneous variations in the velocity of the slice jet being discharged from the headbox cause detrimental variations of the grammage of the final product. These variations occur especially at the rotation frequencies or their multiples of various rotary components. It is also general knowledge that the hydraulic headboxes are particularly sensitive to disturbancies like those described above. It is known that when the velocity of the slice jet increases the absolute magnitude of the velocity variations has to be decreased.
In order to diminish the pressure variations described above, various arrangements and auxiliary equipment have been developed. These can roughly be divided into two main categories. The first category consists of auxiliary equipment which are separate damping devices and are thus not physically connected with the headbox. Devices like this are disclosed in, e.g., U.S. Pat. Nos. 4 116 259, 4 169 757 and 4 308 095, Finnish pat. appl. 137868, U.S. Pat. No. 4 179 332 and Finnish pat. appl. 803048. The second category consists of auxiliary equipment directly attached to the headbox or constituting integral elements of it. Devices like this are disclosed in, e.g., U.S. Pat. Nos. 4 162 189, 4 063 997 and 4 166 759, Finnish pat. appl. 763574 and Swedish pat.appl. 363 652. These known solutions are very costly.